1. Field of the Invention
The present invention relates to a linear recording device which executes optimum writing upon receipt of a series of commands including mixed Read and Write commands, and to a method and a program for executing the same.
2. Description of the Related Art
A tape recording device (a tape drive) is a sequential access device. Drive operations include mount/load and unmount/unload of a tape cartridge. Tape operations include operations on a tape medium which are position movement (a Position command), writing (a Write command), reading (a Read command) and synchronization (a Sinc command: Synchronize).
Data to be written on the tape include user data and a file marker (FM) showing a user data delimiter. A Write operation is performed either in a write-once method in which data is written on the tape from a position behind the end of the last data after the tape is moved, or in an overwrite method in which old data is overwritten with new data.
Normally, the tape drive can perform reading and writing operations in a mixed manner, and these operations involve a moving operation and a synchronization operation (flush). The synchronization and moving operations cause the tape to move in a lengthwise direction thereof, thereby lowering the Read and Write performance of the tape drive. Note that the synchronization operation is an operation of ensuring that data temporarily stored in a buffer is written in a tape medium.
Meanwhile, a hierarchical storage management (HSM) system has the mixed Read and Write operations performed on tape drives.
The tape drive is also included in a tape library which is at a lower layer of the HSM system. A single tape drive, however, is not required to perform Read and Write operations in a mixed manner so that the lowering of the overall performance of the entire read and write processing can be avoided.
Instead, the single tape drive performs either the Write operation or the Read operation for each mount of a tape cartridge. Alternatively, multiple tape drives are each used for either of Write and Read operations. These techniques require more tape drives, increase time-consuming (effort-taking) mount operations, and thus lower the processing performance.
“Castor Monitoring” (available at http://castor.web.cern.ch/castor/presentations/2006/Review/Castor_Monitoring.pdf) and “Tape Efficiency” (available at https://twiki.cern.ch/twiki/pub/FIOgroup/TapeRefCernUsageNov2007/tape_usage_effciency_v05.pdf) illustrate use environments in which a tape cartridge is used exclusively for Read or Write. Large-scaled scientific and technical calculations in particular cannot achieve higher performance, if a single tape cartridge is used for both mixed Read and Write operations. This also holds true for a hierarchical storage system including general tape storage devices.